On the Initiation of the Madden-Julian Oscillation (MJO)


A tropical channel model, defined as a model that is global in the zonal direction but bounded in the meridional direction, is used to study the initiation mechanism of two MJO events. With initial and lateral boundary conditions provided by a global reanalysis, we demonstrate that the simulated MJO initiation does not critically depend on detailed characteristics of sea surface temperature (varying vs. constant in time, mean distribution from boreal spring vs. winter), initial conditions (within a 10 day period), the latitudinal location of the lateral boundaries (21-38 degree N and S), and even latent heating and moist processes. The only factor found critical to the reproduction of the MJO initiation is time varying lateral boundary conditions from the reanalysis indicating the influences from the extratropics.

At the lower troposphere, meridional advection of the zonal (westerly) momentum from the southern Indian Ocean is found to be crucial for the MJO initiation. At the upper troposphere, the time evolution of the wave activity identifies its source over the southern Indian Ocean where it grows by extracting kinetic energy from the mean flow. We further show that it is possible to capture these two MJO events (after years from the model initial time) even in the presence of large error in the mean state. The implications of the results and limitations of the approach will be discussed in the seminar. I will end up with my present work at the IPRC where we are trying to quantify the relative roles of the internal dynamics and the extratropical influences on the MJO.